Movable handling-machines, for example, mobile cranes, are very often equipped with stabilizer beams of variable elongation which extend the frame of the machine laterally and each carry at the end remote from the machine a bearer jack. When the machine has reached its work-station the stabilizer beams are run out to a length compatible with the space available and the vertical bearer jacks connected to the ends of the stabilizer beams are actuated, the downwards movement of the rods of these jacks causing bearer shoes which are fixed to the bottom ends of the jack rods to be placed in contact with the ground. The bearer jacks then lift the machine which no longer rests on the ground other than by means of the bearer jacks.
The stabilizer beams of handling machines generally consist of horizontal beams supporting the bearer jacks, which are mounted to slide inside supporting box-girders integral with the frame of the handling machine.
For such mobile handling-machines employed on unmade-up ground the stabilizer beams equipped with their bearer jacks have disadvantages connected with the fact that the bearer jacks in their closed or inoperative positions (rods returned) at the ends of the stabilizer beams considerably reduce the ground clearance of the machine as may be seen in FIG. 5 representing a bearer jack in the closed position (rod returned) at the end of a supporting box girder of a stabilizer beam of a handling machine. In particular if bearer jacks are needed which have a long stroke in order to achieve levelling of the machine on unmade-up ground, or for use where the differences in level or undulations of the ground may be considerable, the bulk of the jacks in their closed positions becomes such that the ground clearances are insufficient for the handling machine to move about.
The disadvantages are such that they destroy to a great extent the advantages connected with the employment of stabilizer beams of variable elongation, the horizontal arrangement of which enables both a maximum and variable spread of the bearing jacks and a ground clearance compatible with moving about over unmade-up ground, beams furthermore giving the frame excellent rigidity with respect to the ground and the device thus produced being of a low cost price connected with the simplicity of construction.
Additionally, the employment of these machines on any kind of ground necessitates the employment of bearer shoes of large dimensions fixed to the ends of the bearer jack rods. These bearer shoes are so bulky that it is necessary to dismount them when it is required to move the machine. These lengthy and laborious dismantlings are particularly undesirable when the handling machine must be moved frequently. Moreover the bulk of the bearer jack in the position in which it is returned into the supporting box girder of the stabilizer beam reduces the zone of the supporting box girder which may be employed for housing the supporting beam for the jack and thus reduces the maximum possible extension of the levelling members. Finally the bearer jacks which constitute the most important portions of the device as regards the safety of the installation at the time of its levelling in the working position, are directly exposed to impacts and mud spattering when the machine is made to move over bad ground. This may bring about wear and tear of the jacks which are prejudicial to their good operation and therefore to the safety of the installation at the time of its levelling at its working position.